Run integration tests on CP 7 & 8

[loicgreffier]

Recent CP versions have led to some unexpected issues, such as:

• Kafka Connect synchronization breaking due to passwords being hidden in connector configurations
• Describing a consumer group throwing an exception when it does not exist

We should run integration tests on both CP 7 and CP 8.

Useful link:

ns4kafka/src/test/java/com/michelin/ns4kafka/integration/container/KafkaIntegrationTest.java

Line 35 in 4ef4ec0

protected static final String CONFLUENT_PLATFORM_VERSION = "7.7.0";